1. Field of the Invention
The present invention relates to a blue phosphor, and in particular relates to a light emitting device, a cold cathode fluorescent lamp, or a plasma display panel employing the same.
2. Description of the Related Art
Conventional tungsten lamps or fluorescent lamps of white light illumination devices have been gradually replaced by commercially available light emitting diodes (herein after LEDs). Advantages of LEDs are as follows: (1) the small size of LEDs make them suitable to be illumination devices of array packages and collocated with different colors, if necessary; (2) LEDs have relatively long operating life spans of more than 10,000 hours, which is 50 times that of conventional tungsten lamps; (3) LEDs have shock resistance and are durable due to transparent resin being applied as a packaging resin; (4) LEDs are environmentally friendly as the interior structures are free of mercury; (5) LEDs consume ⅓ to ⅕ less power than that of the conventional tungsten lamp.
Generally, white light is a mixture of at least one colored light. For example, the white light seen by a human eye can be formed by mixing blue and yellow lights or mixing blue, green, and red lights. The former white light is a two-wavelength white light, and the latter is tee-wavelength white light white light.
The three most common commercially available semiconductor white light devices are described as follows. The first is a white light illumination device collocated by red, green, and blue LED chips. This white light module has high luminescence efficiency and high color rendering. However, the different colored LED chips require different epitaxial materials, wherein different electrical voltages are needed. Accordingly, the manufacturing cost is high, the circuit layout is complicated, and the appropriate mixing of the different colored lights is difficult.
The second is a white light illumination device disclosed by Nichia Corporation. The most common version is the white light formed by a yellow YAG phosphor excited by a blue LED. The periphery of the blue LED is filled with optical gel sealing the yellow YAG phosphor. The blue LED emits a blue light having a wavelength of about 400 nm to 530 nm. The yellow YAG phosphor is excited by a part of the blue light and then emits a yellow light. The remaining part of the blue light collocates with the yellow light to form a two-wavelength white light.
The described two-wavelength (blue and yellow) white LED has many illumination limitations due to the high color temperatures and uneven colors. Therefore, color quality is less than desired. Next, color control of the white light is difficult due to the blue light wavelength from the LED chip changing along with different temperatures thereof. In addition, the two-wavelength white light lacks red light, thereby reducing color rendering thereof.
The third white light illumination device is formed by blue, green, and red phosphors evenly dispersed in optical gel. After being excited, the phosphors emit red, green, and blue light which further collocate to provide a three-wavelength white light. Although the luminescence efficiency thereof is relatively lower, the three-wavelength white light has high color rendering. Additionally, the manufacturing process of the third white light illumination device is relatively more flexible than that of the first and second white light illumination devices. Most phosphors are sulfide, nitride, or oxide phosphors. While sulfide phosphors usually have high luminescence efficiency, they are also unstable and may easily degrade due to moisture or oxygen. As for nitride phosphors, while they are usually stable, they are also costly due to the difficulty of synthesizing the nitrides in high temperature/pressure conditions.
Please refer to Table 1, which shows the conventional silicate phosphors as disclosed in related patents.
TABLE 1Pat. No.PhosphorsU.S. Pat. No. 6,982,045SrxBayCazSiO4:EuSrxBayCazSiO4:Eu, B(B = Ce, Mn, Ti, Pb, Sn)U.S. Pat. No. 6,943,380(2 − x − y)SrO•x(Ba, Ca)O•(1 − a − b − c −d)SiO2•aP2O5•bAl2O3•cB2O3•dGeO2:yEu2+U.S. Pat. No. 6,939,481(Ba, Sr, Ca)2SiO4:Eu2+U.S. Pat. No. 6,936,857Ca8Mg(SiO4)4C12:Eu2+, Mn2+Sr4Al14O25:Eu2+(SAE)(Tb1−x−yAxREy)3DzO12(YAG/TAG)U.S. Pat. No. 6,809,347(2 − x − y)SrO•x(Ba, Ca)O•(1 − a − b − c −d)SiO2•aP2O5•bAl2O3•cB2O3•dGeO2:yEu2+U.S. Pat. No. 6,776,927CaxSi12−(m+n)Al(m+n)OnN16−n:Euy,DyzU.S. Pat. No. 6,717,353(Sr1−x−aBax)3MgSi2O8:Eua(Y1−a)2SiO5:CeaU.S. Pat. No. 6,657,379Mp/2Si12−p−qAlp+qOqN16−q:Eu2+M = Ca or in combination with Sr or MgU.S. Pat. No. 6,632,379(Cax, My)(Si, Al)12(O, N)16M = Eu, Tb, Yb, ErU.S. Pat. No. 6,621,211A2SiO4:Eu2+A2DSi2O7:Eu2+A includes at least one of Sr, Ca, Ba or MgD includes at least one of Mg or Zn;U.S. Pat. No. 6,504,179Ca8−x−yEuxMnyMg(SiO4)4Cl2x = 0.005~1.6 and y = 0~0.1U.S. Pat. No. 6,429,583Ba2MgSi2O7:Eu2+; Ba2SiO4:Eu2+U.S. Pat. No. 6,294,800Ca8Mg(SiO4)4Cl2:Eu2+, Mn2+U.S. Pat. No. 6,255,670A2DSi2O7:Eu2+Ba2(Mg, Zn)Si2O7:Eu2+(Ba1−x−y−zCaxSryEuz)2(Mg1−w, Znw)Si2O7
The invention provides novel halosilicate phosphors with improved luminescent intensity in comparison with conventional LED phosphors.